Apparatus for regenerating foundry sand

ABSTRACT

Apparatus for the regeneration of foundry sand, particularly sand coated with irreversible inorganic and/or organic binding agents. The sand molds are broken to free the castings and the lumps of hot sand crushed and cooled to ambient temperature. The grains of sand are then separated from the coating of binder and sieved to obtain a selected range of grain sizes equivalent to that of suitable new foundry sand. Grains of sand of excessive size may be pulverised and returned for re-processing. Dust is removed from the sand at one or more of the stages of the process where dust is caused to form. Castings are recovered from the mold fragments by a magnetic or electronic separator.

United States Patent [191 Richard [4 1 Oct. 9, 1979 APPARATUS FORREGENERATING FOUNDRY SAND inventor: Gerard Yves Richard, Precy 7 Disc,France [73] Assignee: will dxpplication de Produits Industriels etChimiques Sarl Department Sigma [221 Filed: Nov. 30, 1971 211 Appl. No.:203,193

[30] Foreign Application Priority Data Primary Examiner-Donald G. KellyAttorney-Robert E. Burns et a1.

[57] ABSTRACT Apparatus for the regeneration of foundry sand,particularly sand coated with irreversible inorganic and- /or organicbinding agents. The sand molds are broken to free the castings and thelumps of hot sand crushed and cooled to ambient temperature. The grainsof sand are then separated from the coating of binder and sieved toobtain a selected range of grain sizes equivalent to that of suitablenew foundry sand, Grains of sand of excessive size may be pulverised andreturned for re-processing. Dust is removed from the sand at one or moreof the stages of the process where dust is caused to form. Castings arerecovered from the mold fragments by a magnetic or electronic separator.

9 Claims, 4 Drawing Figures Patnted Oct. 9, 1973 C: Sheets-Sheet 1Patented Oct. 9, 1973 I5 Sheets-Sheet :3

Patented Oct. 9, 1973 3 Sheets-Sheet 15 APPARATUS FOR REGENERATINGFOUNDRY SAND BACKGROUND OF THE INVENTION This invention relates to aprocess and apparatus for the regeneration of foundry sand; inparticular foundry sand which was prepared with irreversible binderssuch as silicates and organic resins (furan, furan ureaformaldehyde,furan phenol, etc.).

For quite some time the rising price for foundry sand and the problemsarising in foundry sand removal have forced foundrymen to look for waysin which foundry sand could be recovered and re-used in moldingoperations. In the course of time methods have been devised for therecovery of argillaceous sands, synthetic Bentonite sands, cement sandsand finally, with only 50 percent success, sodium silicate processedsands (known as the CO, process or the liquid sand" process).

The development of organic binders like phenolic resins for shellmolding processes and furan resins for no-bake processes has shown theold types of sand recovery units to be unsuitable and that a newtechnique was required for the recovery of burnt sands in which one notonly recovered the sand but in the true sense of the word regeneratedit. If the argilaceous sand reclamation process simply requires abreaking of the lumps, a removal of the gates and risers, and aregrinding and missing with water before re-use, this is not so withsiliceous sands which contain sodium silicate or organic resins (furanand phenolic) as binders. In these two cases the sand becomes coatedwith a layer of mineral binding agent (silicate) or organic bindingagent (resin) and, contrary to clay, this binding agent, as soon as ithas set, becomes inert and thus cannot be re-used. A still more seriousdrawback is the fact that this film of binding agent becomes acontaminant when the sand is simply recuperated, i.e., re-used aftercrushing but without the suitable physical treatment. The fact is thatthe accumulation of carbonates (in the case of the silicate) or ofnitrogen and organic substances (as in the case of resins) rapidlyresults in flaws making it necessary to reject the castings concerned.

In the sphere of regeneration, a first technique has been developed ,inwhich, by way of a new feature, the organic substances undergocalcination, the sand thus acquiring properties similar to its orginalcharacteristics. The technique unfortunately suffers from the drawbackof being extremely expensive, very slow and relatively unproductive. Itis now only used for the sands obtained by the shell molding process,agglomerated with phenolic resins. In the case of the furan resins usedin the no-bake process, owing to the fact that the cost of calcinationis 2.5 times higher than in the case of the phenolic resins, thisprocess cannot be profitably adopted, and the same applies for sodiumsilicate.

PURPOSE OF THE INVENTION The aim of the present invention is toeliminate the foregoing drawbacks, for which purpose it relates to aprocess and an apparatus for the regeneration of foundry sand,particularly of sand prepared with irreversible organic binding agents(sodium silicates) and- /or organic binding agents (e.g., furan resins)of the same type as those used in treatments by the dry method," i.e.,in which the apparatus as in any elementary reclaiming plant, comprisesfirst devices enabling the casting to be separated from the mould bybreaking the latter, and second devices for crushing the fragments ofthe mould, to which first device are added, in particular, devicesenabling mechanical attrition to be carried out, i.e., the separation ofthe film of binding agent in which the grains of sand are encased, thesaid additional devices enabling a completely clean and thoroughlyscreened sand to be obtained, absolutely free of dust.

SUMMARY OF THE INVENTION According to the invention, a process for theregeneration of foundry sand, particularly of sand prepared withinorganic and/or organic irreversible binding agents, comprising initialstages in which the molds are broken and the burning sand crushed, ischaracterized by the fact that the said sand is cooled, in order tobring it to a temperature close to ambient, after which the grains ofsand are separated mechanically from the film of binding agent in whichthey are encased, by simply introducing the said grains into a currentof air, under a high pressure, in such a way that they are flung outagainst the metal side wall of a hermetically sealed casing having avertical axis of symmetry, causing their enclosing matrix to burst,after which a franulometric selection is carried out by means of atleast two screens of different mesh size, restoring the range of grainsizes to that which would be required of an appropriate new sand, thegrains of sand of dimensions included between those of the mesh sizes ofthe two screens then being recuperated, after which the grains of sandtoo large to pass through the screen of greater mesh size and also thosetoo small to pass through the screen of smaller mesh size beingrejected, the sand then being freed of dust in at least one of theplaces, e.g., at the crushing stage, the mechanical separation stage orthe screening stage, where it undergoes a mechanical treatment causingsuch dust to form.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF SPECIFIC EMBODIMENTSThe apparatus for the regeneration of casting sand, particularly sandprepared with irreversible binding agents of the inorganic type (sodiumsilicate) and/or organic type (furan), consists of a conventionalrecuperation apparatus followed by a plurality of additional devicesenabling a sand unsuitable for further use after emerging from theconventional installation to be converted into a sand which recovers itsoriginal character istics, i.e., which for this purpose is cleanedmechanically for the removal of its mineral and/or organic gangue,broken up, screened and freed of dust.

The conventional sand recuperating installation comprises the followingtwo units; a stripping grid 1, which is stationary, vibrating or of theimpact type, its purpose being to break up the mold, enabling thecasting to be recovered at the same time, and a preliminary crusher 2 ofthe hammer jaw or roller type, of which the purpose is to reduce thelarge lumps of sand to finer particles.

The complete sand regenerating plant to which the present inventionrelates comprises a series of new devices which follow the saidconventional installation. in the order in which the grains of sand aretreated the additional installation takes the following form, byreference to FIG. 1:

a. A sand cooling channel 3 cools the burning sand coming from thestripping unit and reduces its temperature to a level close to theambient temperature, this being the only temperature likely to besuitable for the use of sands bound with sodium silicates or organicresins. Any type of cooling apparatus may be used, but that preferred isa continuous cooler based on the fluid bed principle, since theadvantage of a cooler with a metallic fluidization channel resides inthe fact that it makes it possible to avoid the rapid deteriorationsuffered by the conventional rubber conveyor belts as a result of theexcessively hot sand.

b. A belt conveyor 4 or alternatively a vibrating chute, equipped with aseparator for the metallic particles, either of the magnetic type (witha drum or band) for the ferrous metals or of the electronic type for thenon-ferrous metals andthe diamagnetic alloys.

c. An elevator 5 conveying the sand to the upper part of a pneumaticapparatus enabling the sand to be cleaned in order to free it of thefilm of mineral or organic binding agent in which each grain is encased,the apparatus being known as an elutriator" and usable, according to theparticular method selected, as a secondary cooler.

d. An elutriator 6 of which the description will be better understood byreference to FIGS. 3 and 4; this apparatus, with several working stages,consists of a hermetically sealed casing 7 with a vertical axis ofsymmetry (e.g., a cylindrical cone, prism or truncated pyramid) in whicha current of fluid, conveniently air, of medium or high pressure, forcesthe sand which enters through inlet 16 at an even rate from the centreto the walls of the casing 7. ln FIGS. 3 and 4 the air feed conduits 9(fed with air at medium or high pressure) are horizontal and extendacross the casing 7 as far as a general gas supply conduit 13, itselfconnected to a pressure source 14 in the form of a compressor, blower orventilator. Each conduit 9 is provided with orifices, e.g., in the formof narrow longitudinal slots extending over. almost the entire length ofthe conduits 9 and enabling a vigorous horizontal current of gas to beprojected, according to the air layer principle, towards the walls ofthe casing 7, the said current of gas itself carrying along the grainsof sand. Needless to say, the gas could equally be projected by means ofother devices, such as a vertical column having lateral projectionnozzles at each stage, and these projection devices thus form anintegral part of the present invention.

When the grains reach the enclosure 7 they first of all fall by the mereforce of gravity and thus in a direction parallel to the vertical axisof symmetry of the casing, after which they are projected from thecentre towards the walls, in a direction substantially perpendicular tothe said axis, before being intercepted by a set of internal baffles 8which are provided on the wall of the easing and over which the grainsof sand slide, causing a reverse movement of the grains which are thusreturned evenly from the wall to the centre of the casing. Furthermore,a cap 33 is situated above each pressure gas conduit 9 in such a waythat its lower edges 33a contact the plane in which the current of gascirculates at considerable pressure, and the grains of sand which fallby force of gravity and slide along the said cap are immediatelyre-introduced into the current of gas perpendicular to the axis ofsymmetry.

The repeated projection of the sand towards the walls thus breaks theenclosing matrix of binding agent, which is carried along by the currentof air while the sand itself, by the mere force of gravity, drops fromone stage to another in order to undergo a further cleaning process. Thenumber of stages depends solely on the output of the apparatus and onthe extent to which the sand is to be so cleaned.

The elutriator 6 offers advantages by comparison with apparatus whichsimply subjects the sand to mechanical friction, firstly because thecurrent of air separates and removes through dust outlet 11 the dustwhich has been produced, instead of allowing it to flow freely throughthe sand outlet 12 together with the sand, and secondly because theviolent stirring action to which the sand is subjected in the successivecurrents of air results in a by no means negligible reduction in thetemperature of the sand, this temperature being, in practice, reducedfrom C to 40 C.

The air pressure inside the general supply conduit 13 for the elutriator6 is only of relative importance, as it is only the impact created bythe projection of the sand against the wall of the apparatus that has tobe retained. The air pressure at the entry of the elutriator 6 can thusvary according to the cross section of the apparatus (distance to becovered by thesand), the number of stages selected and the hourlydelivery of the sand to be treated. By way of an example, thesenumerical data being in no way limitative, a compromise between the airdelivery, air pressure, wear on the walls, sand cleaning quality, dustremoval and cooling is obtained with an air speed between 15 and 50metres per second and an air delivery between 4 and 12 cubic metres perminute, per ton of sand treated per hour. Furthermore, for sands notsensitive to moisture, such as foundry sands and certain mineralproducts, the cooling qualities of the elutriator can also be improvedby the addition of an atomizer system for the application of very finedrops of volatile liquid such as water, this system being shownschematically by an atomiser 15 situated, for example, verticallyunderneath the sand inlet 16. The atomizer 15 advantageously providedwith means for regulating the water delivery, in order to ensure thefully efficient cooling of the sand by enabling the quantity of waterintroduced to be added to the heat of the sand reaching the elutriator,in such a way as to keep the sand at a constant temperature at itsoutlet 12. By way of an example, a water delivery regulator inside theelutriator is provided in the form of a thermometer for measuring thetemperature of the sand, this thermometer being situated inside or atthe outlet 12 of the elutriator 6, or else in the form of a moisturetesting device which verifies the degree to which the sand has beendried after it has been cooled.

The elutriator 6 thus supplements the crusher 2, of which the action waslimited to that of nullifying the points of connection between thegrains of sand. By projecting the sand at a high speed onto the walls ofthe casing 7 and also by the friction between the grains of sandthemselves, the separation of the sand, grain by grain, is completed bysplitting its coating of binding agent.

e. A screening appparatus 17 with at least two screens, of differentmesh sizes, arranged one above the other. In actual fact thesuperimposed screens will be between two and eight in number. Their mainpurpose is to effect a granulometric selection of the sand to obtain agrain size range covering the same sizes as that of an appropriate newsand, the effect being to render possible the further use of the sandscreened between a maximum and a minimum value as specified for accuratemold and core manufacture.

Screens are selected according to the use the selected sand is to be putafter regeneration, in the same way as grain selection would have beeneffected in order to obtain the most suitable granulometry for a newsand for mold manufacture. The use of multiple screens, which is anoriginal application according to the invention, also makes thefollowing possible:

In the case of two screens, to eliminate the finest grains, startingfrom the screen size regarded as unacceptable. In the case of more thantwo screens, to effect a still finer selection of the sand, bylaccurately regrouping it on the desired screens and eliminating allthose which appear unacceptable.

By way of an example, use can be made of screens arranged in stages, oneabove the other, with successive rejects at each stage, the sizes ofthese screens usually ranging from No. 30 to No. 140, according to theAFS standards.

f. A storage hopper l8, preceding a pneumatic transport device 19 forconveying the grains of sand of which the dimensions areintermediatelthe maximum and minimum determined by the screening device17 of at least two stages. The grains are propelled through tubularconduits 20 to an enclosure where the sand is recuperated and reutilizedfor the manufacture of moulds or cores.

The elimination of the finest grains of sand obtained after thescreening is carried out at the same time as that of the dust, by meansof a device to be described hereinafter. As regards the grains of whichthe dimensions are above the acceptable maximum and which cannot bedirectly re-utilized as such, two solutions are possible, as follows:

l. The coarse rejects can be conveyed through a conduit 21 to asecondary crusher 22 (e.g., a hammer mill or pulverizer) with a hight'circumferential speed, preferably operating at a negative pressure(fordust removal). The purpose of the 'crusher 22 is to supplement, byits action, that of the elutriator 6, thus reducing the size of thegrains of sand and causing their coating of binding agent to burst. Inthe lower part of the crusher 22 the grains of sand are returned to thecycle, in the direction indicated by the arrow 23, starting from thebottom of the elevator 5 in the assembly already described. In theembodiment illustrated the crusher 22 acts solely on the excessivelylarge grains of sand; if desired by the user of the installation,however, it goes without saying that this latter device, installed atthe top of the conveyor 4, can also act on all the grains of sand, evenbefore they are transported by the elevator 5, and simultaneously on thecourse rejects, as described previously, this special arrangement stillbeing within the scope of the principle of the invention on which thepresent installation is based. I

2. The coarse rejects can be conveyed through a conduit 24 into arecuperation hopper 25. The adoption of this alternative path allows acertain number of pieces of agglomerated sand or calibrated granulatesto be recuperated separately, in order to be reutilized in this state,instead of conveying them to the crusher 22 to be reduced to thesuitable grain size; the fact is, particularly for large moulds andcores, that these granulates can be used as very economical fillers,thus economising in the use of silicate or organic binding agents.

g. A dust collection chamber 26, of which the suction intakes aresituated in those places where the sand undergoes a mechanical treatmentliable to cause dust form, i.e., the preliminary crusher 2, the elevator5, the elutriator 6, the screening apparatus 17 and the secondarycrusher 22. The main purpose of the dust removal chamber 26 is to enablea perfectly clean sand to be obtained; for this purpose it differs fromthe hitherto customary dust removal processes, of which the sole purposeis the elimination of the dust liable to be spread to the atmosphere andto render the work unpleasant and dangerous (involving the risk ofsilicosis).

The purpose of the dust removal'chamber 26 is the reason why the suctionintakes (omitted from FIGS. 1 and 2, in order to render the drawingsclearer) are situated in each mechanical treatment device. Consequently,not only the atmosphere will be protected but, above all, the sand willbe freed at its actual source of the dust which is usually carried alongwith it. In the present case the intensity of the dust removal isgoverned by other rules than those usually adopted, and the dust removalchamber 26 consists of a very large suction device taking the form, forexample, of a vertically disposed cylinder in which the air is taken inby suction at the bottom, at the inlet 27, while the air contaminated bythe dust, the finest grains of sand and the coatings of binding agentdetached from the sand grains is removed at the outlet 28, at the top ofthe chamber 26, after filtration, for example, in filter sacks 26a or ina wet separation apparatus.

In addition to the aforementioned units (a) to (g) the complete sandregeneration installation comprises an electric control cabinet (notshown in the drawing) combining the controls for the various items ofapparatus described and rendering them automatic, together with a set ofsafety devices to ensure the satisfactory operation of the plant despitethe shocks caused to the feed system by the mould stripping operation.

Needless to say, the invention is not confined to the method ofapplication or to the constructional version described in the foregoing.Various alternative constructions of the installation are possiblewithout thereby departing from the scope of the invention defined in theappended claims particularly the modified construction shown in FIG. 2of the type of installation already described, there being provided, asseparate units, in an intermediate position between the preliminarycrusher 2 and the cooling channel 3; a'vibrating distributor 29 followedby a separator 30 for recovering the metal parts the latter being eithermagnetic (with a drum or band) for ferrous metals or electronic fornon-ferrous metals and non-magnetic alloys, followed sand from theircoating of binding agent, the said separating means comprising ahermetically sealed casing with a vertical axis of symmetry, and meansfor directing at least one blast of fluid horizontally within the casingwhereby sand falling through the casing is projected against the lateralwalls of the said casing until the matrix of the binding agent is causedto burst, screening means for submitting the separated sand togranulometric selection by at least two screens of different mesh sizesto obtain a granulometric range equivalent to that desired of a newfoundry sand, and means for removing dust from the sand in at least oneof said crushing, separating and screening means where dust is caused toform.

2. Apparatus as claimed in claim I, further including a secondarycrushing apparatus, at least one tubular conduit for conveying grains ofsand of excessive size rejected by said screening means into saidsecondary .crushing apparatus wherein the dimensions of the grains ofexcessive size are reduced and their coating of binding agent caused toburst, and means to enable the grains of sand subjected to the secondarycrushing apparatus to be re-cycled together with those emanating fromthe cooling apparatus whereby grains from both sources are conveyedtogether towards the separating means.

3. Apparatus as claimed in claim 1, wherein there is provided upstreamof the cooling apparatus at least one separator for separating metallicparticles from the sand, said separator being either of the magnetictype for the ferrous metals, or of the electronic type for thenon-ferrous metals and non-magnetic alloys.

4. Apparatus as claimed in claim 1, wherein at least one horizontallydisposed conduit extends through the hermetrically sealed casing, eachconduit being connectable to a source of gas under pressure and havingan orifice whereby at least one horizontal current of gas can beprojected at considerable pressure from each conduit in a directionsubstantially perpendicular to the axis of symmetry of the casing, saidseparating means further comprising a set of internal baffles mounted onthe wall of the casing and on which grains of sand slide evenly from thewall towards the centre of the casing, and a cap mounted above eachpressure gas conduit and of which the lower edge contacts the plane inwhich the current of gas issues from the orifice, whereby grains of sandwhich drop by force of gravity and slide along the said cap areimmediately reintroduced into the current of gas.

5. Apparatus as claimed in claim 4, wherein the separating means furthercomprises at least one atomizer for spraying a volatile liquid to coolthe grains of sand as they enter the separating means.

6. Apparatus as claimed in claim 5, wherein the atomizer is providedwith means for regulating the rate of delivery of the volatile liquid,whereby the quantity thereof can be adjusted according to thetemperature of the sand entering the separating means.

7. Apparatus as claimed in claim 1, including a storage hopper forstoring the grains of sand of acceptable size, the storage hopper beingconnected to a pneumatic conveying device for conveying the grains ofsand.

8. Apparatus as claimed in claim I, further comprising a recuperationhopper for the recuperation and storage of the grains of sand ofexcessive size, the recuperation hopper being connected to the screen ofthe larger grain size by means of a conduit.

9. Apparatus as claimed in claim 1, wherein the dust removal meansconsists of a chamber with a vertical axis of symmetry, the chamberbeing provided with an air intake orifice at the bottom thereof and withan outlet orifice at the top thereof for the evacuation of the aircontaminated with dust, the finest grains of sand and the particles ofbinding agent detached from the grains of sand, means being provided toconnect the said chamber to one or more of the units of the apparatuswhere the sand undergoes mechanical treatment.

1. Apparatus for the regeneration of foundry sand, particularly sand coated with irreversible inorganic and/or organic binding agents, comprising means for breaking sand molds to remove the castings therefrom, means for crushing the hot lumps of sand, cooling apparatus for cooling the crushed sand to ambient temperature, separating means for separating the grains of sand from their coating of binding agent, the said separating means comprising a hermetically sealed casing with a vertical axis of symmetry, and means for directing at least one blast of fluid horizontally within the casing whereby sand falling through the casing is projected against the lateral walls of the said casing until the matrix of the binding agent is caused to burst, screening means for submitting the separated sand to granulometric selection by at least two screens of different mesh sizes to obtain a granulometric range equivalent to that desired of a new foundry sand, and means for removing dust from the sand in at least one of said crushing, separating and screening means where dust is caused to form.
 2. Apparatus as claimed in claim 1, further including a secondary crushing apparatus, at least one tubular conduit for conveying grains of sand of excessive size rejected by said screening means into said secondary crushing apparatus wherein the dimensions of the grains of excessive size are reduced and their coating of binding agent caused to burst, and means to enable the grains of sand subjected to the secondary crushing apparatus to be re-cycled together with those emanating from the cooling apparatUs whereby grains from both sources are conveyed rogether towards the separating means.
 3. Apparatus as claimed in claim 1, wherein there is provided upstream of the cooling apparatus at least one separator for separating metallic particles from the sand, said separator being either of the magnetic type for the ferrous metals, or of the electronic type for the non-ferrous metals and non-magnetic alloys.
 4. Apparatus as claimed in claim 1, wherein at least one horizontally disposed conduit extends through the hermetrically sealed casing, each conduit being connectable to a source of gas under pressure and having an orifice whereby at least one horizontal current of gas can be projected at considerable pressure from each conduit in a direction substantially perpendicular to the axis of symmetry of the casing, said separating means further comprising a set of internal baffles mounted on the wall of the casing and on which grains of sand slide evenly from the wall towards the centre of the casing, and a cap mounted above each pressure gas conduit and of which the lower edge contacts the plane in which the current of gas issues from the orifice, whereby grains of sand which drop by force of gravity and slide along the said cap are immediately re-introduced into the current of gas.
 5. Apparatus as claimed in claim 4, wherein the separating means further comprises at least one atomizer for spraying a volatile liquid to cool the grains of sand as they enter the separating means.
 6. Apparatus as claimed in claim 5, wherein the atomizer is provided with means for regulating the rate of delivery of the volatile liquid, whereby the quantity thereof can be adjusted according to the temperature of the sand entering the separating means.
 7. Apparatus as claimed in claim 1, including a storage hopper for storing the grains of sand of acceptable size, the storage hopper being connected to a pneumatic conveying device for conveying the grains of sand.
 8. Apparatus as claimed in claim 1, further comprising a recuperation hopper for the recuperation and storage of the grains of sand of excessive size, the recuperation hopper being connected to the screen of the larger grain size by means of a conduit.
 9. Apparatus as claimed in claim 1, wherein the dust removal means consists of a chamber with a vertical axis of symmetry, the chamber being provided with an air intake orifice at the bottom thereof and with an outlet orifice at the top thereof for the evacuation of the air contaminated with dust, the finest grains of sand and the particles of binding agent detached from the grains of sand, means being provided to connect the said chamber to one or more of the units of the apparatus where the sand undergoes mechanical treatment. 